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I want to make my own NES cartridge, but I don't know what the correct type of ROM chip would be.

I am specifically thinking about the simplest PCB that works, an NES-NROM-128 which consists of a 16 KiB PRG, and an 8 KiB CHR ROM, like Baseball:

NES Baseball PCB

I assume these are some kind of standard ROM Chip, so I wonder if there are current off-the-shelf chips (preferably EEPROMs so that programming is easy - by which I mean that pulling out the chip and putting it into a programmer is fine, but no UV windows or one-time burn process please) that I can just buy brand new.

And if yes, are they part of a standardized family, so that I could e.g., get a 32 KiB one if I want to make an NES-NROM-256, or a larger one if I find or make a mapper chip?

There's a bunch of EEPROMs on the market, but I'm thinking about stuff like voltage levels, compatible pinout to go directly to the edge connector without a mapper/glue chip, and speed/access times/latency (if that matters - I know if does with some SRAM chips, but no idea about ROM)

(I am ignoring the issue of the 10NES/CIC here, and I am not looking at solutions like Flash Carts - I want to make a "real" NES or Famicom cartridge. I also don't want to reprogram an existing ROM of a donor cart)

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    The question seems to be rather about generic electronic component selection, which is at best borderline for RC.SE - even if tied to a well focused issue. I would assume that there are plenty well staffed NES and game development sites covering NES cartridge designs in all variation.
    – Raffzahn
    Jul 2, 2023 at 11:06
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    There's a fairly comprehensive guide at mousebitelabs.com/2017/06/25/… which includes a table of different size ROM chips. Jul 2, 2023 at 18:13
  • note that you can easily use a bigger (EEP)ROM chip than necessary if you just tie the extra address inputs low. NOR Flash is also likely to be suitable if the timing works out.
    – user253751
    Jul 4, 2023 at 1:34

1 Answer 1

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Drop-in replacements

For the simplest option, seeing as the board that you show uses 24 pin ICs, then I would suggest the following EPROMs, as drop-in replacements:

  • 27C64 (8 kB)
  • 27C128 (16 kB)

27C64 27C128

or the equivalent sized EEPROM:

  • 28C64 (8kB)

28C64

Unfortunately, a 28C128 (16kB) EEPROM doesn't seem to exist, even though pin 26 could have been used for A13.

Obviously, the two pins used for programming the 8 and 16 kB EPROM/EEPROM (pins 1 and 27) should be left unconnected and tied high, respectively.


Larger capacities

You could use even greater capacity EPROMs, still using the same DIP-28 package (with a minor adaptation of the board):

  • 27C256 (32 kB)
  • 27C512 (64 kB)

27C256 27C512

Larger sized EEPROMs have 32 pins, due to the additional pins required for programming/addressing, so other PCB designs would be required:

  • 28256 (32kB)
  • 28512 (64kB)
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  • I have seen 28128 EEPROMs, or at least pinout specifications for them, and they do indeed have A13 on pin 26.
    – cjs
    Jul 3, 2023 at 11:46
  • Yes, I've seen some mentions of them (in forums) during various searches, but no one seems to sell them (any more?) - even second hand on eBay - nor are there any pinouts online that seem to show up. Do you have a link to a pinout? Jul 3, 2023 at 11:48
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    I believe I took the pinout in my notes directly from the JEDEC document. The references there will take you to the JEDEC documentation if you want to try to dig it up. (The documents are free, but you will need to create an account to access them.)
    – cjs
    Jul 3, 2023 at 11:50

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